1. Field of the Invention
The present invention relates to a guide unit which slidably guides a slider with respect to a rail by the rolling of a plurality of rolling units.
2. Description of the Related Art
FIG. 15 to FIG. 26 show a conventional guide unit. This guide unit is disclosed in the Japanese Patent Laid-Open No. 2003-90338 (FIG. 2).
The conventional guide unit shown in FIG. 15 is used, for example, in a straight-line guide part of a machine tool and the like and is constituted by a rail 1 fixed on a fixing part, such as a bed, and a slider 2 which fixes a moving body such as a table.
The above-described slider 2 is constituted by a casing 3, end caps 4, 4 fixed to the casing 3 via spacers 5, 5 before and behind thereof in the sliding direction, and end seals e, e which cover the outsides of the end caps 4, 4. The above-described end caps 4, 4, spacers 5, 5 and end seals e, e are fixed to the casing 3 by means of screws N, N. Also, on the bottom surface of the above-described casing 3 is formed a concavity 2a as shown in FIG. 16. And by inserting the above-described rail 1 in this concavity 2a, the slider 2 is provided so as to cross over the rail 1. Incidentally, the above-described end caps 4, 4, spacers 5, 5 and end seals e, e are also provided with quite the same concavities as the concavity 2a of the casing 3 so as to cross over the rail 1.
On side surfaces 1a, 1a of the above-described rail, there are formed raceway grooves 6a, 6a and holding band clearance grooves 6c, 6c in the axis line direction of the rail 1. As shown in FIG. 16, with the slider 2 crossing over the rail 1, raceway grooves 6b, 6b, which are opposed to the above-described raceway grooves 6a, 6a, are formed on the side surfaces of the casing 3, and these raceway grooves 6b, 6b on the slider 2 side and the above-described raceway grooves 6a, 6a on the rail side jointly constitute raceway paths a, a as shown in FIG. 17.
Furthermore, through holes 7, 7 are formed in the above-described casing 3, and oil retaining sleeves 8, 8 which contain a lubricant are inserted into these through holes 7, 7. The oil retaining sleeves 8, 8 will be described in detail later.
Incidentally, the interiors of the oil retaining sleeves 8 inserted into the above-described through holes 7, 7 constitute a return path c.
On the other hand, as shown in FIG. 18, the above-described end caps 4, 4 have circular arc grooves 4a, 4a and are provided with semicylindrical connections 10a, 10a on one side of these grooves 4a, 4a and with guide projections 20, 20 on the other side thereof.
Above the grooves 4a, 4a there are formed screw holes n, n to insert the screws N, N. And around these screw holes n, n, as shown in FIG. 19, concavities 23, 23 are formed and these concavities 23, 23 are caused to communicate with each other via a first oil groove 21.
The above-described first oil groove 21 communicates with an oil feeding hole 24, and a lubricant is supplied from this oil feeding hole 24 to the first oil groove 21. The lubricant which has been supplied to this first oil groove 21 is guided via the concavities 23, 23 to a second oil groove 22 and supplied from this second oil groove 22 to the grooves 4a, 4a. 
The above-described spacer 5 is, as shown in FIG. 20 to FIG. 23, provided with a pair of passage component members 5a, 5a and the semicylindrical connections 10b, 10b. The passage component members 5a, 5a have circular arc guide surfaces 5c, 5c as shown in FIG. 21. Furthermore, screwholes n, n are formed in the spacers 5, 5.
The spacer 5 constructed as described above is assembled to the end cap 4 as shown in FIGS. 24 and 25. When the spacer 5 is assembled in this manner, as shown in FIG. 17, the grooves 4a, 4a provided in the end cap 4 and the passage component member 5a provided in the spacer 5 jointly constitute U-shaped direction changing paths 9, 9. The direction changing paths 9, 9 formed in this manner cause one opening thereof to communicate with the above-described raceway path a and the other opening thereof to communicate with the above-described return path c. And by ensuring the communication between the raceway path a and the return path c via the direction changing path 9, the raceway path a, direction changing path 9 and return path c jointly constitute an endless circulation path. A large number of metal balls b are put in this circulation path and the balls are caused to perform rolling motions at the contact point between the rail 1 and the slider 2 to maintain smooth movement of the slider 2 with respect to the rail 1.
When the slider 2 moves as described above, the balls b roll in association with the movement. At this time, each ball b circulates continuously via the raceway path a→one direction changing path 9→the return path c→the other direction changing path 9.
Incidentally, as shown in FIG. 17, holding bands 11, 11 are mounted on the casing 3. The holding band 11 is provided to ensure that even when the slider 2 is removed from the rail 1, the balls b do not come off the raceway path a. This holding band 11 enters holding band clearance grooves 6c, 6c when the slider 2 is attached to the rail 1.
In order to maintain high accuracy movement of the slider 2 with respect to the rail 1 for a long period of time in the above-described arrangement, it is necessary not only to reduce the rolling resistance of the balls b, but also to minimize the wear of the rolls b themselves and the wear of the raceway path a and return path c on which the balls b perform rolling motions. For this purpose, it is necessary to periodically or continuously supply a lubricant to the above-described balls b, raceway path a, etc.
In the above-described conventional guide unit, optimum lubrication is maintained by building the oil retaining sleeve 8 which is impregnated with a lubricant into the through hole 7. That is, the above-described oil retaining sleeve 8 is formed from a sintered resin material of porous structure which can contain a lubricant. And the rolling of the balls b within this oil retaining sleeve 8 causes the lubricant which is impregnated in the sleeve 8 to appropriately ooze to the surfaces of the balls b. The rolling of the balls b, to the surfaces of which the lubricant is supplied, on the circulation path causes the lubricant to be supplied also to the whole circulation path.
When the spacer 5 is assembled to the end cap 4 as shown in FIGS. 24 and 25 in the conventional guide unit, the connection 10a provided on the end cap 4 side and the connection 10b provided on the spacer 5 side jointly constitute a positioning cylinder 10.
By inserting the above-described positioning cylinder 10 into the through hole 7, the position of the end cap 4 relative to the casing 3 is determined. When the position of the end cap 4 has been determined in this manner, the centers of the direction changing path 9 and the return path c coincide with each other in their respective connections.
If the center of the connection of the direction changing path 9 deviates from the center of the return path c, it follows that a level difference is produced in a boundary between the direction changing path 9 and the return path c, i.e., the oil retaining sleeve 8. If there is a level difference between the boundary between the direction changing path 9 and the oil retaining sleeve 8, then the balls b strike against the edge surface of the oil retaining sleeve 8 when the balls b pass by the boundary, and the rolling resistance is increased by this striking. The higher the rolling resistance, the more the smooth rolling of the balls b will be impaired, and as a result of this, it becomes impossible to maintain the smooth movement of the slider 2 with respect to the rail 1.
In order to prevent such a disadvantage like this, this conventional guide unit is provided with the positioning cylinder 10 and it is ensured that by use of this positioning cylinder 10 the position of the end cap 4 relative to the casing 3 is accurately determined so that the center of the direction changing path 9 and the center of the return path c coincide with each other.
In the above-described conventional guide unit, the striking of the balls b, which are circulating, against an inner wall part d near the opening of this oil retaining sleeve 8 may sometimes cause the wear of this part. That is, as shown in FIG. 26, a centrifugal force works on the ball b which has passed the U-shaped direction changing path 9 and, therefore, this ball b has a component force F in a direction orthogonal to the axis line A of the oil retaining sleeve 8. Therefore, near the opening where the ball b has rolled into the oil retaining sleeve 8, the above-described component force F remains in this ball b. In this manner, with the component force F caused to remain, the ball b which has rolled into the oil retaining sleeve 8 collides against the above-described inner wall part d near this opening of the oil retaining sleeve 8.
As described above, the oil retaining sleeve 8 has a porous structure because it is necessary to contain a lubricating oil. Therefore, the wear resistance of this oil retaining sleeve 8 is low by the amount corresponding to the porous structure. When the metal ball b collides against this oil retaining sleeve 8, the part where the collision occurred wears. And the wear of the oil retaining sleeve 8 becomes more remarkable when the moving speed of the ball b increases and when the mass of the ball b increases. If the ball b passes the inner wall part d near the opening of the oil retaining sleeve 8 which has worn, the smooth rolling of this ball b is impaired. And when the smooth rolling of the ball b has been impaired like this, this gives rise to the problem that it becomes impossible to maintain the high accuracy movement of the slider 2 relative to the rail 1. There is also another problem that noise is generated when the ball b is passing the worn portion of the oil retaining sleeve 8.
The object of the invention is to provide a guide unit which can prevent the wear of the oil retaining sleeve.